High Hopes for Cassini's Titan Fly-by

NASA's Cassini spacecraft has survived its first plunge through the narrow gap between Saturn's cloud tops and the giant planet's innermost rings, a region that no probe had ever explored before.

The space agency's Deep Space Network Goldstone Complex in California picked up Cassini's signal at 11:56 p.m. PDT yesterday (April 26; 2:56 a.m. EDT and 0656 GMT today, April 27) — nearly a full day after the historic dive took place. Data began coming in from the probe 5 minutes after contact was established, NASA officials said.

"In the grandest tradition of exploration, NASA's Cassini spacecraft has once again blazed a trail, showing us new wonders and demonstrating where our curiosity can take us if we dare," Jim Green, director of the Planetary Science Division at NASA Headquarters in Washington, D.C., said in a statement. [Cassini's 'Grand Finale' Saturn Orbits Explained (Video)] ...

The unmanned Cassini spacecraft, after completing two passes in the vast, unexplored area between Saturn's rings has discovered not much else there, researchers at NASA said.

Scientists have been surprised to find that not all that much—not even space dust—lies between Saturn's iconic rings.

"The region between the rings and Saturn is 'the big empty,' apparently," said Cassini Project Manager Earl Maize of NASA's Jet Propulsion Laboratory in Pasadena, California, after the probe's first pass.

The rings themselves are made of fast-moving particles of ice and space debris.

The 22-foot-tall (6.7 meter) Cassini spacecraft launched in 1997 and began orbiting Saturn in 2004.

Cassini made a first pass to explore what lies between the rings in late April and a second one on May 2, at a speed of about 77,000 miles per hour relative to the planet.

The gap between the rings and the top of Saturn's atmosphere is about 1,500 miles (2,400 kilometers).

Cassini is expected to make a total of 22 dives between the rings and the planet before making a death plunge into the gas giant in September.

Cassini is a 20-year-old joint mission of NASA, the European Space Agency and the Italian Space Agency.

The gaps in the rings are due to gravitational perturbations by Saturn's many moons. It's a resonance effect - if an object orbiting in a particular gap has a period that's a whole number fraction of the period of the controlling moon then it will get regular 'kicks' that will move it away from that gap.

There are similar gaps in the asteroid belts, caused by the gravitational effects of Jupiter, and, to a lesser extent, Saturn.

On Sept. 15, 2017, NASA's Cassini spacecraft will take a suicide plunge into Saturn to avoid contaminating the ringed planet's potentially habitable moons, Titan and Enceladus.

Cassini's fate is tied to the issue of planetary protection, which refers to the measures scientists and engineers take to minimize that chances that life-forms from Earth make it to other worlds. And with NASA's Mars 2020 rover planning to cache samples to one day return to Earth's labs, planetary protection also means making sure that our own world is safe from contamination by possible alien life.

Planetary protection was the first item on the agenda at the Astrobiology Science Conference, which was held last week in Mesa, Arizona. Chemists, biologists, planetary scientists, astronomers and other researchers all vigorously discussed the issue at the meeting's first session on Monday morning (April 24). [5 Bold Claims of Alien Life] ...

Cassini has dived between Saturn and its rings 15 times now, with seven more dives to go, and continues to collect unprecedented science results — along with some spectacular images. In recent statement, NASA spotlighted some of each.

"Cassini is performing beautifully in the final leg of its long journey," Earl Maize, a Cassini project manager at NASA's Jet Propulsion Laboratory in California, said in the statement. "Its observations continue to surprise and delight as we squeeze out every last bit of science that we can get." [NASA's Epic Cassini Mission to Saturn Gets Awesome Video Treatment]

For one, the researchers have found that Saturn's magnetic field has very little tilt; it lines up almost perfectly with the planet's rotation axis. A tilt would have helped researchers determine how long Saturn takes to fully rotate — the length of its "day" — and is what researchers expected to find based on their understanding of how magnetic fields are generated, NASA officials said in the statement. It may be that the tilt is somehow masked by an element in Saturn's atmosphere, they said.

"The tilt seems to be much smaller than we had previously estimated and quite challenging to explain," Michele Dougherty, Cassini's magnetometer investigation lead at Imperial College London, said in the statement. "We have not been able to resolve the length of day at Saturn so far, but we're still working on it." ...

“It’s very positive news for putative-Titan-life studies,” says Jonathan Lunine, a planetary scientist at Cornell University who was not involved in the new study.

Titan has no water, usually considered a prerequisite for life. Instead of water, freezing-cold Titan has liquid methane. There’s even a methane cycle that mimics Earth’s water cycle (SN: 3/21/15, p. 32). But Titan is so cold — usually about –178° Celsius — that the smallest unit of life on Earth, the cell, would shatter in the moon’s subzero seas. ...

NASA's Cassini spacecraft is headed toward its Sept. 15 plunge into Saturn, following a final, distant flyby of the planet's giant moon Titan.

The spacecraft made its closest approach to Titan today at 12:04 p.m. PDT (3:04 p.m. EDT), at an altitude of 73,974 miles (119,049 kilometers) above the moon's surface. The spacecraft is scheduled to make contact with Earth on Sept. 12 at about 6:19 p.m. PDT (9:19 p.m. EDT). Images and other science data taken during the encounter are expected to begin streaming to Earth soon after. Navigators will analyze the spacecraft's trajectory following this downlink to confirm that Cassini is precisely on course to dive into Saturn at the planned time, location and altitude.

This distant encounter is referred to informally as "the goodbye kiss" by mission engineers, because it provides a gravitational nudge that sends the spacecraft toward its dramatic ending in Saturn's upper atmosphere. The geometry of the flyby causes Cassini to slow down slightly in its orbit around Saturn. This lowers the altitude of its flight over the planet so that the spacecraft goes too deep into Saturn's atmosphere to survive, because friction with the atmosphere will cause Cassini to burn up.

Cassini has made hundreds of passes over Titan during its 13-year tour of the Saturn system—including 127 precisely targeted encounters—some at close range and some, like this one, more distant.

"Cassini has been in a long-term relationship with Titan, with a new rendezvous nearly every month for more than a decade," said Cassini Project Manager Earl Maize at NASA's Jet Propulsion Laboratory in Pasadena, California. "This final encounter is something of a bittersweet goodbye, but as it has done throughout the mission, Titan's gravity is once again sending Cassini where we need it to go."

Instead of "energize," a famous "Star Trek: Voyager" cast member has a new command for the almost-finished Cassini mission at Saturn: "Vaporize!"

Robert Picardo, best known for playing an "Emergency Medical Hologram" (doctor) on the TV series "Star Trek: Voyager," belts out a classic opera tune in tribute to Cassini, which will plunge into Saturn's atmosphere on Friday (Sept. 15).

Cassini has been studying Saturn and its moons since 2004; some of its many discoveries include finding at least 101 water geysers spouting from the moon Enceladus and discovering evidence of prebiotic chemistry on the moon Titan. ...

Excellent 1 hour BBC Horizon summarising the whole mission & featuring the scientists & engineers involved. A 30 year mission, 20 years in action. Seems everything worked, meeting or exceeding expectation, for the 20 years, from the getting there via numerous planetary slingshots & a 90 minute engine burn to slow down enough to be captured by Saturn's gravity, Huygens probe landing on Titan, & many other discoveries too numerous to mention here. One of the more unexpected things found were ice 'peaks' 2½ kilometers tall perched on outer rings which are about 30 ft thick.

Absolutely remarkable achievements & they get a bit emotional when it comes to an end crashing into Saturn, like the death of a loved one. Some of them had spent virtually their whole working life on it. It's in high def which is worth it for the photos. Recommended.

The NASA Saturn probe fired its thrusters full bore for at least 91 seconds during its suicide plunge into the ringed planet on Sept. 15, battling hard to keep its antenna pointed at Earth for as long as possible, mission team members said.

"Given that Cassini wasn't designed to fly into a planetary atmosphere, it's remarkable that the spacecraft held on as long as it did, allowing its science instruments to send back data to the last second," Cassini project manager Earl Maize, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, said in a statement. "It was a solidly built craft, and it did everything we asked of it." [In Photos: Cassini's Last Views of Saturn at Mission's End]

Cassini has been studying Saturn and its moons since 2004; some of its many discoveries include finding at least 101 water geysers spouting from the moon Enceladus and discovering evidence of prebiotic chemistry on the moon Titan. ...

Microbes that produce methane may already be living on Enceladus, a moon of Saturn which is tipped to host life because it boasts a liquid water ocean beneath a crust of solid ice, and strange atmospheric plumes of water. That’s the implication of research showing that an earthbound organism which also produces methane can happily survive in conditions known to exist on Enceladus, from observations by the Cassini space probe before its mission ended last year.

Isolated from deep sea vents almost 1000 metres deep in the Okinawa Trough off Japan, Methanothermococcus okinawensis was subjected to gruelling physical and chemical conditions found on Enceladus for more than five years.